Acetaminophen And Codeine and Pentazocine: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jun 30, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Acetaminophen And Codeine
Pentazocine
No brand names on record
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
These two pain medicines can work against each other and can also add up in risky ways. Pentazocine is a special kind of opioid that can actually block some of codeine's pain relief. If you already take codeine, adding pentazocine may make your pain worse or even trigger withdrawal feelings like sweating, chills, and stomach upset.
At the same time, both drugs calm the brain and body. Together they can cause heavy sleepiness, slow breathing, low blood pressure, and, in rare cases, a serious reaction called serotonin syndrome. Please don't stop or change anything on your own. Your doctor or pharmacist can pick a safer plan and watch you closely.
Direction: Pentazocine is a mixed opioid agonist/antagonist. When combined with codeine (a full mu-agonist prodrug activated by CYP2D6 to morphine), it competitively binds opioid receptors and can reduce codeine's analgesic effect and precipitate withdrawal. Separately, additive serotonergic and CNS-depressant effects raise risk.
- Effects: blunted analgesia/withdrawal, plus serotonin syndrome, hypotension, respiratory depression, profound sedation, coma, death.
- Evidence: theoretical; severity major; onset unspecified.
- Management: avoid combination; reserve for inadequate alternatives. Use lowest dose/shortest duration, monitor for sedation and respiratory depression, especially at initiation/titration. Discontinue codeine if serotonin syndrome suspected; consider naloxone.
What happens
Reduced analgesic effect and/or precipitation of withdrawal symptoms, an increased risk of serotonin syndrome and an increased risk of hypotension, respiratory depression, profound sedation, coma, and death
Interaction Deep Dive
Codeine should not be taken together with pentazocine, which acts as a serotonergic CNS depressant and functions as a mixed opioid agonist/antagonist or partial agonist opioid analgesic, because this combination can diminish codeine's analgesic effect and potentially trigger withdrawal symptoms, heighten the likelihood of serotonin syndrome, and raise the risk of hypotension, respiratory depression, profound sedation, coma, and death. Prescribing these two agents together should be limited to patients for whom other treatment options prove inadequate. Keep both the doses and the treatment durations at the lowest levels necessary. Monitor patients carefully for indications of respiratory depression and sedation. When combined use is justified, observe the patient closely, especially at the start of therapy and when adjusting the dose. Should serotonin syndrome be suspected, stop codeine, and consider prescribing naloxone for emergency management of opioid overdose1.
Why it happens (mechanism)
Competitive binding at opioid receptors; additive serotonergic effects; additive CNS depression
How to manage this interaction
The safest approach is usually to avoid using these two together. Your care team will generally reserve this combination only for situations where other options aren't enough.
- Keep taking both exactly as prescribed. Do not start, stop, or change either one on your own.
- If they are used together, your team may use the lowest dose for the shortest time and watch you more closely, especially when starting or adjusting.
- Tell your prescriber or pharmacist right away about worsening pain, withdrawal feelings, heavy drowsiness, slow breathing, dizziness, agitation, fever, or tremors.
- Your team may also discuss having naloxone on hand.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Acetaminophen And Codeine and Pentazocine together?
Combining codeine with pentazocine can reduce codeine's pain relief, trigger withdrawal, and add up to dangerous sedation, slow breathing, and serotonin syndrome, so this pairing is best avoided unless your care team specifically manages it. Talk with your doctor or pharmacist before using both. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Acetaminophen And Codeine and Pentazocine interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Acetaminophen And Codeine and Pentazocine interaction managed?
The safest approach is usually to avoid using these two together. Your care team will generally reserve this combination only for situations where other options aren't enough. Keep taking both exactly as prescribed. Do not start, stop, or change either one on your own. If they are used together, your team may use the lowest dose for the shortest time and watch you more closely, especially when sta… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
Questions for your pharmacist
- Does my dose of Acetaminophen And Codeine or Pentazocine need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (1)
- Product Information: CARISOPRODOL, ASPIRIN, CODEINE PHOSPHATE oral tablets, carisoprodol, aspirin, codeine phosphate oral tablets. Ingenus Pharmaceuticals LLC (per DailyMed), Orlando, FL, 2021. DailyMed
Keep reading about Acetaminophen And Codeine
Keep reading about Pentazocine
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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